This invention relates to agricultural tractors.
The traveling speed of the agricultural tractor has to be adjusted to different ranges depending on the load received at a ground engaging implement attached thereto. Where an ordinary rotary plow is attached to engage the ground and the load is relatively small, the tractor may travel at a relatively high speed for efficiency of operation. Where a trencher or the like is attached for deep plowing which causes a great load, the tractor needs to travel at a considerably slow speed compared with the case of an ordinary rotary plow. To enable the tractor to be operable for both, the transmission system leading from the engine to drive wheels must include a speed change mechanism adapted to provide a reduction ratio far greater than a maximum reduction ratio provided by a speed change mechanism capable of ordinary range reductions. If the tractor is integrally provided with such a speed change mechanism, the whole tractor construction will become large and very costly. Therefore, in conventional practice tractors intended specially for slow travelling and having a different construction from ordinary tractors are manufactured. It involves manufacture of a speed change mechanism adapted to provide a reduction ratio for low speed range in a separate process from manufacturing a speed change mechanism for the ordinary tractor; the two speed change mechanisms generally have very different constructions. Besides a transmission case different from the type for the ordinary tractor is manufactured, then the speed change mechanism for slow traveling is fitted in the transmission case, and finally they are are assembled with other components. Thus, the two types of tractors require entirely separate production lines at least for manufacture of the speed change mechanism and the transmission case, and for placing the speed change mechanism in the transmission case. This has the disadvantage of poor productivity and high manufacturing cost as a whole.